Although theoretically hydraulic cylinders which are connected in a series-flow relationship and are matched with respect to fluid capacities operate simultaneously and in equal amounts when subjected to pressurized fluid, it has been found that in some situations such ideal operation is not obtained and, in fact, one or more cylinders in the series may drift out of its intended position. For example, where such a system is utilized on a tillage implement to control working depth of tools associated with the implement by raising and lowering the frame relative to the ground, it has been noted that even though the master cylinder in the series may stop at its intended location such that proper depth of operation is achieved at that portion of the frame, other cylinders in the series which are slaved to the master may have a tendency to drift away from the depth thought to be established by the master. It is believed that such drift is caused at least in part by factors such as expansibility of hoses used in the hydraulic circuit; compressibility, though slight, of the hydraulic fluid; differences in pressures experienced in the system when operating at high flow rates as compared to lower flow rates; temperature and viscosity of the fluid; leakage of the primary tractor control valve; and the manner in which the tractor valve is actually manipulated by the operator, e.g., whether or not the valve is held in an open position for a certain amount of time beyond that which is actually necessary for the implement to reach its selected depth of operation.